What's the aluminum foil for? I have thought about layering with a thick viscous material for damping if needed. Plumbers putty in strips in between sheets of foam board or cardboard might work? My first back loaded horns were cardboard.

Has anyone considered or tried using a 'smart' material like a non-newtonian liquid (cornstarch and water) as damping material in speakers? It responds by stiffening up like a hard solid when subjected to rapid time-varying shear stress. Silly putty (or Dow Corning 3179 dilitant compound) is a nice silicone based version of this type of material. It can be made to solid-like properties by combining with polyurethane foam so that it doesn't flow like a liquid under gravity, a commercially made material called D3O uses 3179 as the core ingredient in armor pads for crash protection. A laminate of thinner MDF or aluminum and D3O would be an interesting cabinet material. It would preferentially absorb higher frequencies and can be tuned by varying composition. A simple DIY test with silly putty would be interesting though.

I finally installed the VifaTC9FD's into the wall hanging 'picture' speakers. I hooked it up to the Lepai amp and iPod and tested with a variety of tracks. They sound fantastic, I mean really good. The bass is really nice, and the mids and highs have really good detail. The biggest surprise was the imaging given that they are mounted only about 2 feet apart in the same box as a stereo set. It is my first full range point source speaker and I just can't get over how good a pair of tiny 3.5 inch $12 dollar speakers and a box made of foam core paper and old pillow stuffing can sound. I am a true believer in full range drivers and TL's now. I am hearing details and sounds that I never knew were there before. The Vifa drivers are super in case anyone else hasn't heard them. Here is a photo of the new speaker propped onto some stools for testing. I need to have them decorated and put a picture frame wire for hanging on the back.

My next project for the Vifa TC9FD is a back loaded horn. This design is tuned for about 70 Hz based on a 48 in path length. I am using the plumbers putty in a sandwich between foam core for the front baffle to reduce any high frequencies that may re-radiate from the front. The enclosure is 5 in wide by 10 in deep by 15 in tall, as usual, the size is chosen to maximize cuts based on 20 x30 foam core stock. I am lightly stuffing some bends to clean out the highs from leaking thru. The driver chamber is heavily stuffed and has a throat area equal to the driver piston area, the expansion is modest, only about 5.7 to 1 but that is all the room I had in a bookshelf design. I pre installed some lamp cord straight thru - no binding posts for these cheapy projects.